1. Field of the Invention
The invention relates to a state-of-charge detector device, a program thereof, and a full charge determining method. More particularly, the invention relates to a state-of-charge detector device for detecting the state of charge of a secondary battery, and a program that causes a computer to function as a secondary battery charge-discharge determining device, as well as a state-of-charge detecting method for detecting the state of charge of a secondary battery, and a charge-discharge control device for controlling the charging and discharging of a secondary battery.
2. Description of the Related Art
Conventionally proposed devices of the aforementioned type for detecting the state of charge of a secondary battery include a device that detects a fully charged state of a secondary battery on the basis of an inter-terminal voltage, and a device that detects a fully charged state of a secondary battery on the basis of a fall of the inter-terminal voltage. The former device detects the fully charged state of a secondary battery when the inter-terminal voltage of the battery reaches a predetermined threshold value. The latter device detects the fully charged state when the inter-terminal voltage of the secondary battery decreases by at least a predetermined amount after increasing to a peak. Therefore, it is considered possible to prevent the overcharge of a secondary battery by controlling the charging of the secondary battery so that the secondary battery will not be charged beyond the fully charged state detected as described above.
However, in some cases, the former device, which detects the fully charged state on the basis of the inter-terminal voltage, has a drawback as follows. That is, the degree of rise of the inter-terminal voltage of a secondary battery when the battery is reaching the fully charged state becomes small depending on the kind of secondary battery, such as an alkaline type battery (Ni-MH battery or the like) or the like. In such a case, the discrimination of the inter-terminal voltage with reference to the predetermined threshold value is likely to have an error, and therefore the device cannot precisely determine whether the battery has reached the fully charged state. The latter device, which detects the fully charged state when the inter-terminal voltage of a secondary battery has decreased by a predetermined amount after reaching a peak, has a drawback as follows. That is, in some cases, a distinguished peak of the inter-terminal voltage does not appear. In such cases, the device will face difficulty in detecting the fully charged state. There exist other devices which detect the fully charged state of a secondary battery on the basis of the deviation between the temperature of the secondary battery and an ambient temperature utilizing the fact that the temperature of a secondary battery rises as the battery approaches the fully charged state, or which detect the fully charged state of a secondary battery on the basis of the time-based rising rate of the temperature of the secondary battery. However, the temperature of a secondary battery is considerably affected by various factors, such as the configuration of the battery, the heat capacity thereof, the charging speed, the heat generation based on internal resistance, etc. Therefore, it is very difficult for these devices to detect the fully charged state of a secondary battery with high precision under precise condition setting.